WO 2011/058344 A1 describes a solenoid actuator. The solenoid actuator includes a permanent magnet which provides a bias which can allow fewer amp turns to be used. Thus, a smaller coil cross section and a shorter magnetic path length may be used which can help to reduce magnetic leakage which in turn can mean that even fewer amp turns can be used.
Although the solenoid actuator described in WO 2011/058344 A1 ibid. has advantages over solenoid actuators without a permanent magnet, such as the potential to provide greater opening force, further improvements can be made.